This invention relates generally to printers, typewriters and other image-placing equipment which utilize precut sheets, illustratively of paper, as the image receiving medium, and more particularly to printers in which the characters are formed serially.
As offices and individuals increasingly operate computer-based equipment from remote locations, including printers for producing hard copy on paper for later inspection, there is a corresponding need to exchange information and files and to share equipment. Wired networks are often provided for permitting communication between several users so that they may share information and input/output facilities. However, in situations where a hard copy output device, such as a printer, is operated by a remote user, overall system reliability can be severely degraded by a lack of a human attendant at the printer site. This is particularly true where the printer is designed to be operated primarily under the supervision of a local operator who can monitor the equipment. It is, however, inefficient to station an operator at equipment which only intermittently needs attention, especially since it is practically impossible to predict exactly when such equipment will require a human attendant.
It is a known problem that remote printer equipment often needs attention, but the need for such attention is unpredictable and difficult to schedule. The present art includes automatic cut sheets feeders, but only local inspection can determine the size of the paper in the automatic feeder, and whether the number of sheets of that size paper, in stock in the feeder is likely to satisfy the remote order to print out Q sets of R pages. Oftentimes, a remote attendant or operator can schedule a smaller existing job to consume the available paper supply and plan to visit and reload the feeder input hopper before the large job is printed.
In addition, there are several printer adjustment tasks that optimize printing on a given type of paper and such printer adjustments cannot be performed conveniently without leaving the user's normal workstation and visiting the site of the printer. With a serial impact printer, illustratively a disc printer, in which the character to be printed is mounted at the periphery of one of approximately one hundred spokes connected to a common circular hub, a hammer is electrically signaled to engage the rear of the character-bearing pad and urge the pad into a ribbon so that the ink layer atop the ribbon assumes the shape of the desired character and is then impressed onto the paper to form the visible character mark. To secure a character image with high density, sharp edge definition, and unbroken dark area fill between the edge boundaries may require that the printer be adjusted precisely for the particular paper being used.
The throat opening of a printer is a zone located between the ribbon and the paper-holding platen. This throat opening distance must be adjusted so that it is just greater than the paper thickness. Hammer impact energy is varied, usually on the basis of character size and/or paper thickness information, and the distance between the rest position of the hammer to its probable impact point.
It is a further problem that multiple paper sets or very thick paper will absorb more energy than thin paper. There is therefore a need for a strike-receiving member, such as an impact bar or platen, with the capability of selectable resiliency and/or hardness for optimizing the clarity of print on a variety of paper thicknesses. Multipart sets using microencapsulated ink which prints on all pages after the first in a set are known, and require substantial printing parameter changes. The prior art has thrust at this problem in manual typewriters by making the whole platen roll interchangeable, using a medium durometer hardness rubber platen roll for 20 to 30 pound basis weight paper, and a brass platen for use in printing on 60 pound basis weight paper, such as library cards and the like.
The determination of the location of the edge of the paper stock which has been fed into the printing zone is at least as important as the aforementioned printing parameters. When paper is automatically fed into a printer, it is usually necessary to ensure that the left edge of the paper is aligned vertically so that the printing lines are substantially horizontal. A multiplicity of optical or mechanical sensors are known in the art, such as a method whereby an illuminator source and detector are mounted on the laterally moving print carriage. However, in systems where the edge is sensed by comparing the paper reflectance against a provided background, the use of a light-absorptive or dark paper stock may confuse the edge measurement detector when the comparison is perfomed against a dark background. It is preferable to use an edge detection system that does not contact or damage the paper, and this is a significant advantage of an all-optical system. Accordingly, there is a need for an optical edge location system which is reliable when working with dark paper stock.
It is important to determine the location of the left paper edge, so that the internal margin control can reconstruct a desired margin width after vertical realignment of paper thereof. Such realignment is generally likely to shift the paper laterally on the platen wlth respect to its original position. Thus, after vertical alignment, it is possible dynamically to relocate the actual printing margins according to edge location measurement, assuming that the paper edge can be accurately located.
It is, therefore, an object of this invention to provide a printer with an edge location measurement system which is markedly less sensitive to paper color and absorptivity than previous visible light reflectance systems.
It is another object of this invention to provide a printer with a gauging system with which paper supply quantity can be measured; the results of this measurement being transmitted to a remote location so that a user at that location can control printing without visiting the printer site.
It is a further object of this invention to use the gauging system-derived value of paper stock thickness so that the printer throat distance can be automatically adjusted for optimum printing distance.
It is still another object of this invention to use the gauging system-derived value of paper stock thickness so that hammer parameters can be reset for optimum print quality.
It is yet another object of this invention to use the gauging system-derived value of paper stock thickness so that the effective platen hardness may be altered to achieve optimum printing.